Lubrication system

ABSTRACT

A method for reducing the presence of ferritic particles in lubricant employed in the lubrication of rotary shaft bearing of the type that include a first bearing contact surface, a second bearing contact surface and a plurality of rotatable bearing members disposed therebetween, a lubrication system employing such method and a lubricated assembly. The method includes providing a ferritic particle collector element of magnetised material in close proximity to the bearing and a path of lubricant flowing to the bearing. The close proximity being within a distance from the bearing contact surface which is less than five times the maximum diameter of the bearing contact surfaces. The collecting element may be an existing component of a lubrication system or lubricated assembly which is rendered magnetic or may be a magnet or magnets secured to an existing component.

BACKGROUND OF THE INVENTION

This invention relates to a lubrication system and in particular,although not exclusively, to a lubrication system for a gear unit, and agear unit comprising a lubrication system, wherein said gear unitcomprises a plurality of rotatable components rotatably supported byrotary shaft bearings such as ball bearings or roller bearings.

In a gear unit, as well as other types of lubricated equipment, thecleanliness of the oil is one of the most important factors influencingthe life time of the bearings. In a method of bearing calculationaccording to ISO 281 standard, and in combination with a service lifefactor (a_(xyz)) dependent on load and contamination, the factor for thecontamination varies from 0 to 1. For dip or splash lubricated gearunits, the factor can never become 1 because there is no possibility ofeffective filtration. In the case of force lubricated gear units using afilter to improve cleanliness and reduce the contamination, significantexpense is involved because micro filters must be used to get a goodcontamination factor approaching 1.

In contaminated oil it is primarily only hard particles that decreasethe working life of the bearing. Normally those particles are of steeland arise from wear occurring during use. It is known to employ oil sumpdrain plugs of the kind incorporating a magnet to collect suchparticles, but generally these are of only poor effectiveness becausethe magnet is of only small size.

SUMMARY OF THE INVENTION

The present invention seeks to provide a lubrication system and alubricated assembly comprising a lubrication system in which potentiallydamaging contaminant particles are more effectively and efficientlyremoved than hitherto. It seeks also to provide lubricated equipment,such as gear unit, having an enhanced working life.

In accordance with aspects of the present invention there is provided alubricated assembly a lubrication system and a method for reducing thepresence of ferritic particles in a lubricant employed for thelubrication of a rotary shaft bearing of the type comprising a firstbearing contact surface, a second bearing contact surface and aplurality of rotatable bearing members disposed therebetween, wherein acollector element of magnetized material is provided in close proximityto the bearing and the path of lubricant flowing to the bearing, saidcollector element being provided at a distance from said bearing contactsurfaces which is less than 5 times the maximum diameter of said bearingcontact surfaces.

Preferably the distance of the collector element from said bearingcontact surfaces is less than 3 times the maximum diameter of saidbearing contact surfaces.

The bearing may be primarily a radial type bearing, in which case saidmaximum diameter will be defined by the maximum contact surface diameterof the outer bearing ring or cup. The bearing may be primarily an axialtype bearing, in which case both of the first and second contactsurfaces will define a substantially common maximum diameter, or it maybe of a type with transmits both axial and radial loads, in which caseone of the two contact surfaces will define said maximum diameter.

The bearing members may for example be in the shape of a ball, or aroller such as of a cylindrical or frusto-conical shape.

The present invention further teaches that in lubricated equipmentcomprising a plurality of rotary shaft bearings, at least two of therotary shaft bearings are in said proximity to a collector element. Ifthe two bearings are sufficiently close to one another they may be inclose proximity to a common collector element Alternatively, and also inthe case of bearings more widely spaced, each have said two bearings mayhave a respective collector element associated therewith.

In the case of equipment having dip or bath type lubrication it ispreferred that the collector element is spaced from the bearing contactsurfaces by a distance less than the maximum diameter of said bearingcontact surfaces, more preferably less than half of that distance.

In the case of equipment having splash lubrication, preferably splashedoil or like lubricant is guided to the bearing via a lubricant collectorand channel system. In that case the collector element of magneticmaterial may be provided as part of the lubrication collection systemand channel, and preferably at a distance from the bearing element lessthan 3 times the maximum diameter of said bearing contact surfaces.

The structure of the collector element may be comprised by aconventionally provided component of a gear unit, such as a bearingcover cap or seal but which, in accordance with the present invention isrendered magnetic either by being formed of material which is, or iscaused to become, magnetic, or to which a magnet is secured.

Thus, in the case of a rotary shaft bearing supported by the outerhousing wall of a lubricated assembly such a gear unit, and wherein thehousing wall is provided with a selectively moveable bearing cap, saidbearing cap may comprise the collector element of magnetised material. Ametal component of or serving as the bearing cap may be of magnetisedmaterial, or a permanent magnet may be secured to the bearing cap. Anouter surface of a bearing cap may be provided with a coating ofpolymeric material, such rubber, so as to prevent the outer surface ofthe housing undesirably collecting ferritic particles.

In the case of a lubricated assembly which employs splash lubricationand is provided with a lubricant collecting box in which splashedlubricant is collected for feeding to a bearing, the collecting box maybe comprised of magnetised material or have a permanent magnet securedthereto. Preferably an outer surface of the box exposed to the splashflow is provided with a polymer coating thereby to enhance the degree towhich ferritic particles are arrested within the lubricant collectingbox and thus are less exposed to displacement during extreme operatingconditions such as when the flow of splash lubricant is temporarily at ahigher than normal velocity.

In the case of lubricated equipment which is a multi-stage gear unit itis preferred that a collector element of magnetised material is providedin said close proximity to each of the bearings of a low speed shaft,and preferably also in close proximity to at least an adjacentintermediate shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying diagrammatic drawingsin which;

FIG. 1 is a cross-sectional view of part of a gear unit having alubrication system in accordance with the present invention;

FIG. 2 is a cross-sectional view of part of another gear unit having alubrication system in accordance with the present invention;

FIG. 3 is a cross-sectional view of part of a further gear unit having alubrication system in accordance with the present invention;

FIG. 4 is a cross-sectional view of part of a gear unit employing asplash lubrication system in accordance with the present invention;

FIG. 5 is a cross-section of part of yet another gear unit which employsa splash lubrication system in accordance with the present invention;

FIG. 6 is a cross-sectional view of part of a gear unit showing thelower end region of a vertically mounted shaft, and

FIG. 7 is a cross-sectional view of part of a gear unit having a shaftend supported by two bearings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows part of a gear unit 10 having a housing outer wall 11 whichsupports a bearing 12 in which a shaft 18 is rotatably mounted. Thebearing 12 is a roller bearing comprising rollers 13 which maintainspaced apart relatively rotatable inner and outer bearing contactsurfaces 12B, 12A.

The bearing 12 is located in a through-bore 19 in the housing wallwhereby if necessary the bearing can be fitted or removed fromexternally of the gear unit. A bearing cover cap 14 fits tightly in thethrough-bore 19 and seals against leakage of the oil lubricant 16.

The bearing cover cap 14 is of a laminated construction comprising amagnetised steel cap having a central disc portion 20 and an axiallyinwardly extending flanged edge 21. The outer surface of the diskportion is provided with a rubber coating 28 which also extends over andencapsulates the flanged edge 21. Said rubber material assists inproviding a fluid seal between the flanged edge of the cap and thethrough-bore 19, as well as resisting unwanted collection of ferriticparticles on the external surface of the bearing cover cap 14.

In use of the gear unit, oil 16 tends inherently to flow axially throughthe bearing 12 in a direction from the chamber 22 defined by the spacebetween the end of the shaft 18 and the bearing cover cap 14. In thisembodiment the axial space between the bearing cover cap 14 and thebearing 12 at the end of the shaft 18 is approximately one third of thediameter of the bearing outer contact surface 12A. Thus the magnetisedsteel of the bearing cover plate is in close proximity to the bearing ata position in the direction of flow of oil to the bearing, and it isthereby found possible to effectively arrest ferritic particles fromflowing into the bearing and causing damage to the bearing rollers 13 orthe bearing contact surfaces 12A, 12B.

FIG. 2 shows a modification of the embodiment of FIG. 1 in which theneed to magnetise the steel of the bearing cover cap 14 is avoided bythe use instead of a permanent magnet 30 secured to the bearing covercap 14. In this construction it is not necessary that the bearing covercap comprise a steel insert, and it may alternatively comprise areinforcing insert of non magnetisable material.

FIG. 3 show a further variation of the invention as applied to a bearing40 mounted in a gear unit housing outer wall 41 for support of a shaft42 that extends through the housing wall. In this construction anannular lip seal 43 is located within the bore 44 of the housing walland provides a fluid seal against the outer surface 46 of the shaft 42.The lip seal comprises an annular reinforcing element 45 which may be ofsteel and magnetised so as to perform a particle collection function inthe same manner as the magnetised steel of the end cap described withreference to FIG. 1. Alternatively a permanent magnet may be secured tothe lip seal, irrespective of whether the lip seal is reinforced by anelement of magnetisable or non magnetisable material, such that thepermanent magnet can serve to collect ferritic particles in the samemanner as described above with reference to FIG. 2.

In FIG. 4 there is shown part of the multi stage gear unit 50 comprisinga low speed shaft 51 rotatably supported by taper roller bearings 52, 53mounted in respective spaced side walls 54, 55 of the gear unit housing56. The housing comprises a cover plate 57 which supports, within thelubricated chamber of the gear unit housing, an oil collecting box 59.The oil collecting box 59 is positioned in a manner known per se tocollect oil splashed upwards from a pinion 60 mounted on the shaft, andis arranged to direct the flow of collected oil sideways and downwardsto collection zones 61 from which oil feeds through respective apertures62 into the space between an end of the shaft 51 and outer bearing cover63. In this embodiment the oil collecting box is formed from pressedsteel which has been magnetised, and the surface of the steel facingtowards the pinion wheel is provided with a rubber coating 64 wherebyferritic partlicles contained within splashed oil tend inherently toaccumulate within the oil collecting box.

FIG. 5 shows a variation of the embodiment of FIG. 4 in which the oilcollecting box is formed either of non magnetised material or nonmagnetisable material. Contained within the box 60 is a permanent magnet61 for collection of ferritic particles. As in respect of the FIG. 4embodiment, a surface of the collecting box facing towards the pinionwheel may be provided with a rubber or like coating to resist collectionof ferritic particles at that surface of the collecting box.

FIG. 6 shows the lower end region 70 of a vertically mounted shaft 71supported by a bearing 72 which primarily provides axial location of theshaft 71 relative to the gear unit housing 73. The shaft end andbearing, in use, are immersed in sump oil 74. Radial location of theshaft 71 is provided by a pair of axially spaced ball bearings (notshown), one of which may be positioned in the oil sump and the other ofwhich may be located above the sump and, for example, be of a sealedtype pre-filled with a grease lubricant. The bearing 72 is located in abore 75 of the housing wall which also locates an annular abutment ring76 for the outer bearing cup 77. The bore 75 is sealed by a rubbercovered end cap 78 to the inner surface of which is secured a permanentmagnet 79. In this embodiment the spacing of the magnet 79 from thebearing 72 is less that the maximum outer diameter of the bearingcontact surface 80 of the bearing cup 77.

FIG. 7 shows a horizontally mounted shaft 90 rotatably supportedrelative to a bore 91 in a gear unit housing 92 by means of an axialload bearing 93 and a radial load bearing 94. A cap 95 and seal 96 closethe bore 91 against leakage of oil. In this embodiment a permanentmagnet 97 is secured to a surface 98 of the housing wall in closeproximity to the axial load bearing 93.

As compared with the conventional procedure of providing an oil drainplug with a magnet, or magnetisable material, and which is remote frommany of the lubricated surfaces in a lubricated assembly, the presentinvention achieves a very much enhanced ability to arrest flow offerritic particles before damage occurs. In consequence it is possibleto achieve a substantially improved load and contamination factor foruse in calculating bearing life according to ISO 281. Servicing andreplacement part costs are thereby reduced, and this is achieved withoutthe need to employ expensive micro filters. The additional expenditurerequired by the present invention is confined to either magnetising ofmaterial already employed in a lubricated assembly such as gear unit orproviding permanent magnets, and optionally rubber coatings toselectively resist accumulation of ferritic particles at selectedsurface regions.

1. A method for reducing the presence of ferritic particles in alubricant employed for the lubrication of a gear unit comprising aplurality of rotary shaft bearings of the type comprising a firstbearing contact surface, a second bearing contact surface and aplurality of rotatable bearing members disposed therebetween, saidmethod comprising: placing a ferritic particle collector element ofmagnetized material adjacent to each of at least two of said pluralityof rotary shaft bearings and a path of lubricant flowing to saidplurality of rotary shaft bearings; and spacing each of said at leasttwo of said plurality of rotary shaft bearings at a distance from arespective collector element so that corresponding first and secondbearing contact surfaces are less than five times the maximum diameterof said first and second bearing contact surfaces.
 2. The methodaccording to claim 1, wherein said step of spacing said at least two ofsaid plurality of rotary shaft bearings comprises spacing the respectivecollector element from said corresponding first and second bearingcontact surfaces less than three times the maximum diameter of saidfirst and second bearing contact surfaces.
 3. The method according toclaim 1, wherein the step of spacing said at least two of said pluralityof rotary shaft bearings comprises spacing the respective collectorelement from the corresponding first and second bearing contact surfacesby a distance of less than the maximum diameter of said first and secondbearing contact surfaces.
 4. The method according to claim 1, whereinthe step of spacing said at least two of said plurality of rotary shaftbearings comprises spacing the respective collector element from thecorresponding first and second bearing contact surfaces by a distance ofless than half of the maximum diameter of said first and second bearingcontact surfaces.
 5. A gear unit lubrication system for reducing thepresence of ferritic particles in a lubricant employed for thelubrication of a gear unit comprising: plural rotary shaft bearingscomprising a first bearing contact surface, a second bearing contactsurface and a plurality of rotatable bearing members disposedtherebetween; and a ferritic particle collector element of magnetizedmaterial provided adjacent to each of at least two of the plural rotaryshaft bearings and a path of lubricant flowing to the plural rotaryshaft bearings, wherein a distance from a respective collector elementto corresponding first and second bearing contact surfaces of each ofsaid at least two of the plural rotary shaft bearings is less than fivetimes the maximum diameter of said first and second bearing contactsurfaces.
 6. The lubrication system according to claim 5, wherein saiddistance is less than three times the maximum diameter of said first andsecond bearing contact surfaces.
 7. The lubrication system according toclaim 5 wherein the collector element is rendered magnetic either bybeing formed of a magnetic material or a material which is caused tobecome magnetic.
 8. The lubrication system according to claim 6 whereinthe collector element further comprises a magnet secured thereto.
 9. Thelubrication system according to claim 5 wherein selected parts of thelubrication system are provided with a coating of a polymeric materialto prevent those parts undesirably collecting ferritic particles. 10.The gear lubrication system according to claim 5, wherein the distancefrom the respective collector element to the corresponding first andsecond bearing contact surfaces is less than the maximum diameter ofsaid first and second bearing contact surfaces.
 11. The gear lubricationsystem according to claim 5, wherein the distance from the respectivecollector element to the corresponding first and second contact bearingsurfaces is less than half of the maximum diameter of said first andsecond bearing contact surfaces.
 12. The gear lubrication systemaccording to claim 5, wherein said at least two of said plurality ofrotary shaft bearings are each associated with a respective separatecollector element.
 13. The gear lubrication system according to claim 5,wherein said at least two of said plurality of rotary shaft bearings areeach associated with a common collector element.
 14. The gearlubrication system according to claim 5, wherein the collector unit isformed by or is contained within an oil collecting box of the gear unit.15. The gear lubrication system according to claim 5, wherein thecollector element comprises a selectively moveable bearing cap providedin an outer housing wall of the gear unit.
 16. The gear lubricationsystem according to claim 5, wherein the collector element is formed byor is contained within a seal.
 17. A lubricated gear unit assemblycomprising a gear unit lubrication system according to claim 5.